I'm looking at camera systems again. What makes Pentax special? I recall that they have APS-C + sensor shift shake compensation, right? So it's sorta like Olympus crossed with canon/nikon.

As Richard has said, plenty of other brands have users who'll say what makes them special. For me there are a few things that keep me with Pentax:

Size/weight. For me they are in the Goldilocks zone: nearly all Canon/Nikon models are too big; Olympus and the MLCs are too small. Pentax bodies are just right: enough to get hold of in a hand (as opposed to finger and thumb) but still compact.

Ergonomics. In my family we range from MF film through FF DSLRs down to 4/3 and even my Pentax Q as well as a few P&Ss. The Pentax system of buttons, wheels and menus feels the most logical and intuitive. It's hard to explain but the impression is always that Pentax cameras are designed by photographers who know the difference between key controls and nice add-ons.

Lenses. I've always preferred using primes to zooms. The Pentax Limited primes are excellent and compact.

Price. A big differentiator when I moved to digital; less so now but Pentax is still relatively cheap for equivalent quality across the board (although it's possible to cherry pick individual items where Pentax is more expensive).

One qualification: the Pentax flash system is very weak in comparison to Nikon and relatively weak compared to Canon. It's also more expensive. If I were a dedicated studio professional I wouldn't use Pentax - but I'm not and I do.